For hundreds of years, cod swarmed in waters off Newfoundland's rugged coast. But by 1992, rampant overfishing had crushed the cod. Price tag to people: tens of thousands of jobs lost and billions of dollars spent in job retraining.

Last year, a weather satellite spotted a monster dust cloud over Africa - hard to miss at 5,000 miles wide. Tree-cutting in northern Africa helps nourish such clouds, which cross the Atlantic, settle into US coastal waters, and possibly contribute to toxic algae blooms. Price tag to people: breathing problems for US coastal residents.

Cod depletion and dust clouds seem like pretty different problems. But they each play a role in the overall environmental degradation of the planet - a condition that a new global study says has escalated so quickly over the past 50 years that it outpaces anything experienced by ecosystems in human history.

Demands for water, food, fuel, timber, and fiber - all part of global economic expansion - have driven the change. The result: a big increase in short-term human benefits, less hunger, and more wealth. But this progress has been counterbalanced by a massive loss of diversity of life on Earth.

That's the state of the world, according to the first Millennium Ecosystem Assessment produced by some 1,300 scientists from 95 countries charged with painting a global eco-portrait. The United Nations-sponsored study was funded by the World Bank and several private foundations.

"We've had many reports on environmental degradation, but for the first time we're now able to draw connections between ecosystem services and human well-being," says Cristian Samper, director of the Smithsonian Institution's National Museum of Natural History in Washington and a chief architect of the study.

Northern Africa's drying Sahel region and Newfoundland's emptier coastal waters, he says, are just two examples in an overall conclusion that 60 percent of the world's ecosystems are being degraded or used unsustainably. Ecosystems being drained or degraded largely in the pursuit of human well being include:

• Land: More of it has been converted to crop land since 1945 than in the 18th and 19th centuries combined. Cultivated land now covers one-quarter of Earth's land surface.

• Coral reefs: About 20 percent of the world's coral reefs were lost and another 20 percent degraded in the past few decades.

• Rivers and lakes: Despite the fact that the amount of fresh water stored behind dams has quadrupled since 1960, its use for agriculture and other needs has exceeded long-term supplies by 5 to 25 percent.

• Coastal areas: Farmers' increased use of nitrogen fertilizers since 1985 has polluted waterways and coastal ecosystems. About 35 percent of mangrove swamps needed for water filtration in coastal areas have been bulldozed.

• Oceans: Many areas have been overfished, reducing stocks by 90 to 99 percent of preindustrial fishing levels.

"We always have this sense that if we just let up on overfishing for awhile the fish will bounce back," says Tundi Agardy, executive director of Sound Seas, a coastal-planning policy group, who was lead author on the coastal chapter of the millennium assessment. "But what we found is that, many times, the recovery of overexploited species is made impossible by all sorts of things like pollution, habitat loss, and climate change."

The loss of coral, for instance, is often attributed to degraded coastal waters that were harmed over time. Mangrove swamps that filter pollutants were bulldozed for apartment buildings. Combine that with large human populations living seaside and increased agricultural runoff flowing into the oceans. Now add overharvesting of fish that eat algae. Suddenly, you've got algae blooms that overwhelm coral reefs, Dr. Agardy says.

It's not known what changes have kept the cod from rebounding. Some say a change in ocean salinity. Others, including former fishermen, have blamed seals for eating them. Harp seal pups were butchered on the ice this spring for their pelts, but also in the expectation that a smaller seal population would help the cod recover.

But in years past, the cod recovered even with seal predators present, Agardy says. "It's pretty clear that cod have been fished down to a point where it will be hard for them to ever recover," she adds.

Yet changes in fishing policy and enforcement of those changes may help oceans recover, she says, adding that the question now is whether the political will exists to create change.

A key element of the UN report was to bring together economists and biologists to examine the impact of ecosystem changes on human well-being. In accounting terms, the report says, the loss of an ecosystem can be equated to loss of a capital asset.

For instance, exploitation of nature has benefited the economies of nations like Ecuador, Kazakhstan, Democratic Republic of Congo, and Venezuela. But those nations actually experienced a "loss in net savings" when depletion of natural resources (energy and forests) and damage from carbon emissions were factored in, the report found.

A key finding was that abrupt, unexpected changes in ecosystems are increasingly likely. Changes are usually gradual in ecosystems, yet once a threshold is crossed, stark and rapid changes are possible.

Susan Minnemeyer spotted one of those changes a few years ago while peering for the first time at sharp satellite photos of Cameroon's dense tropical rain forest. As global information systems manager for Global Forest Watch project at the World Resources Institute in Washington, she noticed tiny lines in the forest, a spider's web criss-crossing the jungle - thousands of miles of illegal logging roads.

Losing valuable forest to illegal logging is bad enough, she notes, but another critical hidden cost has emerged: loss of wildlife.

Superficially, the Cameroon forest looks intact even after such logging because the forests aren't clear-cut; just the valuable trees are taken. But the illegal roads have opened up paths for hunters.

The growth of the bushmeat trade is rapidly depopulating the forests of all large mammals, Ms. Minnemeyer says. Her finding was just one of many examples of accelerating species loss cited in the study.

"It can look intact from the sky," Ms. Minnemeyer says. "But this is an empty forest - it's actually devoid of wildlife. We think we can change this, and we're working with the government to do that."